Various types of pressure sensing systems for monitoring the pressure within the tires of a vehicle generate a pressure signal using an electromagnetic signal, which is transmitted to a receiver. The pressure signal corresponds to the pressure within a tire. When the tire pressure monitoring system detects a low pressure situation, the vehicle operator is directed to remedy the problem. Such problems are remedied by replacing the low tire with a spare tire, or filling the low tire to increase the pressure therein.
Many vehicles are designed as “split placard” vehicles. This means that the vehicles are designed to operate with tire pressures for the front tires that are different than tire pressures for the rear tires. In order to warn a vehicle operator that the tire pressure in a tire is significantly under-inflated relative to the pressure suggested by the OEM, the tire pressure monitoring system (TPMS) must be capable of identifying the tire and associating it with the location of the wheel. This identification and association becomes slightly more complicated when applied to “split placard” vehicles.
In an initiator based TPMS, a controller activates an initiator closest to the wheel location for which a sensor is being identified. The initiator then transmits a low frequency signal to the sensor in the wheel. The sensor detects the low frequency signal and responds by transmitting a signal back to the controller. Ideally, the sensor in closest proximity to the initiator will respond. However, observations of this system have shown that multiple sensors may respond to a single initiator signal. This phenomenon is often called “cross talk”. In the event cross talk occurs, the controller has no additional information, or means, to properly select the correct sensor ID to associate to the wheel location.
One method for attempting to eliminate cross talk has been addressed in the initiator. An initiator that is capable of focusing its transmitted energy to a very narrow region has been developed. The narrow region is constrained to include only the expected range of sensor locations for a desired sensor. This solution is not very practical, nor is it cost effective, in that each initiator must be designed for a specific vehicle model and wheel location. For a variety of body styles this would require an initiator design for each body style. Ultimately this solution is not cost effective when applied to mass produced vehicles because it creates the need to have multiple parts to support different body styles.
There is a need to solve the cross talk problem without the need to focus the signal which requires customizing each initiator, adding unwanted cost and complexity to the component.